/**
 * @file
 *
 * Neighbor discovery and stateless address autoconfiguration for IPv6.
 * Aims to be compliant with RFC 4861 (Neighbor discovery) and RFC 4862
 * (Address autoconfiguration).
 */

/*
 * Copyright (c) 2010 Inico Technologies Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Ivan Delamer <delamer@inicotech.com>
 *
 *
 * Please coordinate changes and requests with Ivan Delamer
 * <delamer@inicotech.com>
 */

#include "lwip/opt.h"

#if LWIP_IPV6 /* don't build if not configured for use in lwipopts.h */

#include "lwip/nd6.h"
#include "lwip/priv/nd6_priv.h"
#include "lwip/prot/nd6.h"
#include "lwip/prot/icmp6.h"
#include "lwip/pbuf.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/ip6.h"
#include "lwip/ip6_addr.h"
#include "lwip/inet_chksum.h"
#include "lwip/netif.h"
#include "lwip/icmp6.h"
#include "lwip/mld6.h"
#include "lwip/dhcp6.h"
#include "lwip/ip.h"
#include "lwip/stats.h"
#include "lwip/dns.h"

#include <string.h>

#ifdef LWIP_HOOK_FILENAME
#include LWIP_HOOK_FILENAME
#endif

#if LWIP_IPV6_DUP_DETECT_ATTEMPTS > IP6_ADDR_TENTATIVE_COUNT_MASK
#error LWIP_IPV6_DUP_DETECT_ATTEMPTS > IP6_ADDR_TENTATIVE_COUNT_MASK
#endif

/* Router tables. */
struct nd6_neighbor_cache_entry neighbor_cache[LWIP_ND6_NUM_NEIGHBORS];
struct nd6_destination_cache_entry destination_cache[LWIP_ND6_NUM_DESTINATIONS];
struct nd6_prefix_list_entry prefix_list[LWIP_ND6_NUM_PREFIXES];
struct nd6_router_list_entry default_router_list[LWIP_ND6_NUM_ROUTERS];

/* Default values, can be updated by a RA message. */
u32_t reachable_time = LWIP_ND6_REACHABLE_TIME;
u32_t retrans_timer = LWIP_ND6_RETRANS_TIMER; /* @todo implement this value in timer */

/* Index for cache entries. */
static u8_t nd6_cached_neighbor_index;
static netif_addr_idx_t nd6_cached_destination_index;

/* Multicast address holder. */
static ip6_addr_t multicast_address;

static u8_t nd6_tmr_rs_reduction;

/* Static buffer to parse RA packet options */
union ra_options {
    struct lladdr_option lladdr;
    struct mtu_option mtu;
    struct prefix_option prefix;
#if LWIP_ND6_RDNSS_MAX_DNS_SERVERS
    struct rdnss_option rdnss;
#endif
};
static union ra_options nd6_ra_buffer;

/* Forward declarations. */
static s8_t nd6_find_neighbor_cache_entry(const ip6_addr_t* ip6addr);
static s8_t nd6_new_neighbor_cache_entry(void);
static void nd6_free_neighbor_cache_entry(s8_t i);
static s16_t nd6_find_destination_cache_entry(const ip6_addr_t* ip6addr);
static s16_t nd6_new_destination_cache_entry(void);
static int nd6_is_prefix_in_netif(const ip6_addr_t* ip6addr, struct netif* netif);
static s8_t nd6_select_router(const ip6_addr_t* ip6addr, struct netif* netif);
static s8_t nd6_get_router(const ip6_addr_t* router_addr, struct netif* netif);
static s8_t nd6_new_router(const ip6_addr_t* router_addr, struct netif* netif);
static s8_t nd6_get_onlink_prefix(const ip6_addr_t* prefix, struct netif* netif);
static s8_t nd6_new_onlink_prefix(const ip6_addr_t* prefix, struct netif* netif);
static s8_t nd6_get_next_hop_entry(const ip6_addr_t* ip6addr, struct netif* netif);
static err_t nd6_queue_packet(s8_t neighbor_index, struct pbuf* q);

#define ND6_SEND_FLAG_MULTICAST_DEST 0x01
#define ND6_SEND_FLAG_ALLNODES_DEST  0x02
#define ND6_SEND_FLAG_ANY_SRC        0x04
static void nd6_send_ns(struct netif* netif, const ip6_addr_t* target_addr, u8_t flags);
static void nd6_send_na(struct netif* netif, const ip6_addr_t* target_addr, u8_t flags);
static void nd6_send_neighbor_cache_probe(struct nd6_neighbor_cache_entry* entry, u8_t flags);
#if LWIP_IPV6_SEND_ROUTER_SOLICIT
static err_t nd6_send_rs(struct netif* netif);
#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */

#if LWIP_ND6_QUEUEING
static void nd6_free_q(struct nd6_q_entry* q);
#else /* LWIP_ND6_QUEUEING */
#define nd6_free_q(q) pbuf_free(q)
#endif /* LWIP_ND6_QUEUEING */
static void nd6_send_q(s8_t i);

/**
 * A local address has been determined to be a duplicate. Take the appropriate
 * action(s) on the address and the interface as a whole.
 *
 * @param netif the netif that owns the address
 * @param addr_idx the index of the address detected to be a duplicate
 */
static void nd6_duplicate_addr_detected(struct netif* netif, s8_t addr_idx)
{

    /* Mark the address as duplicate, but leave its lifetimes alone. If this was
     * a manually assigned address, it will remain in existence as duplicate, and
     * as such be unusable for any practical purposes until manual intervention.
     * If this was an autogenerated address, the address will follow normal
     * expiration rules, and thus disappear once its valid lifetime expires. */
    netif_ip6_addr_set_state(netif, addr_idx, IP6_ADDR_DUPLICATED);

#if LWIP_IPV6_AUTOCONFIG
    /* If the affected address was the link-local address that we use to generate
     * all other addresses, then we should not continue to use those derived
     * addresses either, so mark them as duplicate as well. For autoconfig-only
     * setups, this will make the interface effectively unusable, approaching the
     * intention of RFC 4862 Sec. 5.4.5. @todo implement the full requirements */
    if (addr_idx == 0)
    {
        s8_t i;
        for (i = 1; i < LWIP_IPV6_NUM_ADDRESSES; i++)
        {
            if (!ip6_addr_isinvalid(netif_ip6_addr_state(netif, i)) && !netif_ip6_addr_isstatic(netif, i))
            {
                netif_ip6_addr_set_state(netif, i, IP6_ADDR_DUPLICATED);
            }
        }
    }
#endif /* LWIP_IPV6_AUTOCONFIG */
}

#if LWIP_IPV6_AUTOCONFIG
/**
 * We received a router advertisement that contains a prefix with the
 * autoconfiguration flag set. Add or update an associated autogenerated
 * address.
 *
 * @param netif the netif on which the router advertisement arrived
 * @param prefix_opt a pointer to the prefix option data
 * @param prefix_addr an aligned copy of the prefix address
 */
static void nd6_process_autoconfig_prefix(
    struct netif* netif,
    struct prefix_option* prefix_opt,
    const ip6_addr_t* prefix_addr)
{
    ip6_addr_t ip6addr;
    u32_t valid_life, pref_life;
    u8_t addr_state;
    s8_t i, free_idx;

    /* The caller already checks RFC 4862 Sec. 5.5.3 points (a) and (b). We do
     * the rest, starting with checks for (c) and (d) here. */
    valid_life = lwip_htonl(prefix_opt->valid_lifetime);
    pref_life = lwip_htonl(prefix_opt->preferred_lifetime);
    if (pref_life > valid_life || prefix_opt->prefix_length != 64)
    {
        return; /* silently ignore this prefix for autoconfiguration purposes */
    }

    /* If an autogenerated address already exists for this prefix, update its
     * lifetimes. An address is considered autogenerated if 1) it is not static
     * (i.e., manually assigned), and 2) there is an advertised autoconfiguration
     * prefix for it (the one we are processing here). This does not necessarily
     * exclude the possibility that the address was actually assigned by, say,
     * DHCPv6. If that distinction becomes important in the future, more state
     * must be kept. As explained elsewhere we also update lifetimes of tentative
     * and duplicate addresses. Skip address slot 0 (the link-local address). */
    for (i = 1; i < LWIP_IPV6_NUM_ADDRESSES; i++)
    {
        addr_state = netif_ip6_addr_state(netif, i);
        if (!ip6_addr_isinvalid(addr_state) && !netif_ip6_addr_isstatic(netif, i)
            && ip6_addr_netcmp(prefix_addr, netif_ip6_addr(netif, i)))
        {
            /* Update the valid lifetime, as per RFC 4862 Sec. 5.5.3 point (e).
             * The valid lifetime will never drop to zero as a result of this. */
            u32_t remaining_life = netif_ip6_addr_valid_life(netif, i);
            if (valid_life > ND6_2HRS || valid_life > remaining_life)
            {
                netif_ip6_addr_set_valid_life(netif, i, valid_life);
            }
            else if (remaining_life > ND6_2HRS)
            {
                netif_ip6_addr_set_valid_life(netif, i, ND6_2HRS);
            }
            LWIP_ASSERT("bad valid lifetime", !netif_ip6_addr_isstatic(netif, i));
            /* Update the preferred lifetime. No bounds checks are needed here. In
             * rare cases the advertisement may un-deprecate the address, though.
             * Deprecation is left to the timer code where it is handled anyway. */
            if (pref_life > 0 && addr_state == IP6_ADDR_DEPRECATED)
            {
                netif_ip6_addr_set_state(netif, i, IP6_ADDR_PREFERRED);
            }
            netif_ip6_addr_set_pref_life(netif, i, pref_life);
            return; /* there should be at most one matching address */
        }
    }

    /* No autogenerated address exists for this prefix yet. See if we can add a
     * new one. However, if IPv6 autoconfiguration is administratively disabled,
     * do not generate new addresses, but do keep updating lifetimes for existing
     * addresses. Also, when adding new addresses, we must protect explicitly
     * against a valid lifetime of zero, because again, we use that as a special
     * value. The generated address would otherwise expire immediately anyway.
     * Finally, the original link-local address must be usable at all. We start
     * creating addresses even if the link-local address is still in tentative
     * state though, and deal with the fallout of that upon DAD collision. */
    addr_state = netif_ip6_addr_state(netif, 0);
    if (!netif->ip6_autoconfig_enabled || valid_life == IP6_ADDR_LIFE_STATIC || ip6_addr_isinvalid(addr_state)
        || ip6_addr_isduplicated(addr_state))
    {
        return;
    }

    /* Construct the new address that we intend to use, and then see if that
     * address really does not exist. It might have been added manually, after
     * all. As a side effect, find a free slot. Note that we cannot use
     * netif_add_ip6_address() here, as it would return ERR_OK if the address
     * already did exist, resulting in that address being given lifetimes. */
    IP6_ADDR(
        &ip6addr,
        prefix_addr->addr[0],
        prefix_addr->addr[1],
        netif_ip6_addr(netif, 0)->addr[2],
        netif_ip6_addr(netif, 0)->addr[3]);
    ip6_addr_assign_zone(&ip6addr, IP6_UNICAST, netif);

    free_idx = 0;
    for (i = 1; i < LWIP_IPV6_NUM_ADDRESSES; i++)
    {
        if (!ip6_addr_isinvalid(netif_ip6_addr_state(netif, i)))
        {
            if (ip6_addr_cmp(&ip6addr, netif_ip6_addr(netif, i)))
            {
                return; /* formed address already exists */
            }
        }
        else if (free_idx == 0)
        {
            free_idx = i;
        }
    }
    if (free_idx == 0)
    {
        return; /* no address slots available, try again on next advertisement */
    }

    /* Assign the new address to the interface. */
    ip_addr_copy_from_ip6(netif->ip6_addr[free_idx], ip6addr);
    netif_ip6_addr_set_valid_life(netif, free_idx, valid_life);
    netif_ip6_addr_set_pref_life(netif, free_idx, pref_life);
    netif_ip6_addr_set_state(netif, free_idx, IP6_ADDR_TENTATIVE);
}
#endif /* LWIP_IPV6_AUTOCONFIG */

/**
 * Process an incoming neighbor discovery message
 *
 * @param p the nd packet, p->payload pointing to the icmpv6 header
 * @param inp the netif on which this packet was received
 */
void nd6_input(struct pbuf* p, struct netif* inp)
{
    u8_t msg_type;
    s8_t i;
    s16_t dest_idx;

    ND6_STATS_INC(nd6.recv);

    msg_type = *((u8_t*)p->payload);
    switch (msg_type)
    {
    case ICMP6_TYPE_NA: /* Neighbor Advertisement. */
    {
        struct na_header* na_hdr;
        struct lladdr_option* lladdr_opt;
        ip6_addr_t target_address;

        /* Check that na header fits in packet. */
        if (p->len < (sizeof(struct na_header)))
        {
            /* @todo debug message */
            pbuf_free(p);
            ND6_STATS_INC(nd6.lenerr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        na_hdr = (struct na_header*)p->payload;

        /* Create an aligned, zoned copy of the target address. */
        ip6_addr_copy_from_packed(target_address, na_hdr->target_address);
        ip6_addr_assign_zone(&target_address, IP6_UNICAST, inp);

        /* Check a subset of the other RFC 4861 Sec. 7.1.2 requirements. */
        if (IP6H_HOPLIM(ip6_current_header()) != ND6_HOPLIM || na_hdr->code != 0
            || ip6_addr_ismulticast(&target_address))
        {
            pbuf_free(p);
            ND6_STATS_INC(nd6.proterr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        /* @todo RFC MUST: if IP destination is multicast, Solicited flag is zero */
        /* @todo RFC MUST: all included options have a length greater than zero */

        /* Unsolicited NA?*/
        if (ip6_addr_ismulticast(ip6_current_dest_addr()))
        {
            /* This is an unsolicited NA.
             * link-layer changed?
             * part of DAD mechanism? */

#if LWIP_IPV6_DUP_DETECT_ATTEMPTS
            /* If the target address matches this netif, it is a DAD response. */
            for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++)
            {
                if (!ip6_addr_isinvalid(netif_ip6_addr_state(inp, i))
                    && !ip6_addr_isduplicated(netif_ip6_addr_state(inp, i))
                    && ip6_addr_cmp(&target_address, netif_ip6_addr(inp, i)))
                {
                    /* We are using a duplicate address. */
                    nd6_duplicate_addr_detected(inp, i);

                    pbuf_free(p);
                    return;
                }
            }
#endif /* LWIP_IPV6_DUP_DETECT_ATTEMPTS */

            /* Check that link-layer address option also fits in packet. */
            if (p->len < (sizeof(struct na_header) + 2))
            {
                /* @todo debug message */
                pbuf_free(p);
                ND6_STATS_INC(nd6.lenerr);
                ND6_STATS_INC(nd6.drop);
                return;
            }

            lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct na_header));

            if (p->len < (sizeof(struct na_header) + (lladdr_opt->length << 3)))
            {
                /* @todo debug message */
                pbuf_free(p);
                ND6_STATS_INC(nd6.lenerr);
                ND6_STATS_INC(nd6.drop);
                return;
            }

            /* This is an unsolicited NA, most likely there was a LLADDR change. */
            i = nd6_find_neighbor_cache_entry(&target_address);
            if (i >= 0)
            {
                if (na_hdr->flags & ND6_FLAG_OVERRIDE)
                {
                    MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
                }
            }
        }
        else
        {
            /* This is a solicited NA.
             * neighbor address resolution response?
             * neighbor unreachability detection response? */

            /* Find the cache entry corresponding to this na. */
            i = nd6_find_neighbor_cache_entry(&target_address);
            if (i < 0)
            {
                /* We no longer care about this target address. drop it. */
                pbuf_free(p);
                return;
            }

            /* Update cache entry. */
            if ((na_hdr->flags & ND6_FLAG_OVERRIDE) || (neighbor_cache[i].state == ND6_INCOMPLETE))
            {
                /* Check that link-layer address option also fits in packet. */
                if (p->len < (sizeof(struct na_header) + 2))
                {
                    /* @todo debug message */
                    pbuf_free(p);
                    ND6_STATS_INC(nd6.lenerr);
                    ND6_STATS_INC(nd6.drop);
                    return;
                }

                lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct na_header));

                if (p->len < (sizeof(struct na_header) + (lladdr_opt->length << 3)))
                {
                    /* @todo debug message */
                    pbuf_free(p);
                    ND6_STATS_INC(nd6.lenerr);
                    ND6_STATS_INC(nd6.drop);
                    return;
                }

                MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
            }

            neighbor_cache[i].netif = inp;
            neighbor_cache[i].state = ND6_REACHABLE;
            neighbor_cache[i].counter.reachable_time = reachable_time;

            /* Send queued packets, if any. */
            if (neighbor_cache[i].q != NULL)
            {
                nd6_send_q(i);
            }
        }

        break; /* ICMP6_TYPE_NA */
    }
    case ICMP6_TYPE_NS: /* Neighbor solicitation. */
    {
        struct ns_header* ns_hdr;
        struct lladdr_option* lladdr_opt;
        ip6_addr_t target_address;
        u8_t accepted;

        /* Check that ns header fits in packet. */
        if (p->len < sizeof(struct ns_header))
        {
            /* @todo debug message */
            pbuf_free(p);
            ND6_STATS_INC(nd6.lenerr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        ns_hdr = (struct ns_header*)p->payload;

        /* Create an aligned, zoned copy of the target address. */
        ip6_addr_copy_from_packed(target_address, ns_hdr->target_address);
        ip6_addr_assign_zone(&target_address, IP6_UNICAST, inp);

        /* Check a subset of the other RFC 4861 Sec. 7.1.1 requirements. */
        if (IP6H_HOPLIM(ip6_current_header()) != ND6_HOPLIM || ns_hdr->code != 0
            || ip6_addr_ismulticast(&target_address))
        {
            pbuf_free(p);
            ND6_STATS_INC(nd6.proterr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        /* @todo RFC MUST: all included options have a length greater than zero */
        /* @todo RFC MUST: if IP source is 'any', destination is solicited-node multicast address */
        /* @todo RFC MUST: if IP source is 'any', there is no source LL address option */

        /* Check if there is a link-layer address provided. Only point to it if in this buffer. */
        if (p->len >= (sizeof(struct ns_header) + 2))
        {
            lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct ns_header));
            if (p->len < (sizeof(struct ns_header) + (lladdr_opt->length << 3)))
            {
                lladdr_opt = NULL;
            }
        }
        else
        {
            lladdr_opt = NULL;
        }

        /* Check if the target address is configured on the receiving netif. */
        accepted = 0;
        for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i)
        {
            if ((ip6_addr_isvalid(netif_ip6_addr_state(inp, i))
                 || (ip6_addr_istentative(netif_ip6_addr_state(inp, i)) && ip6_addr_isany(ip6_current_src_addr())))
                && ip6_addr_cmp(&target_address, netif_ip6_addr(inp, i)))
            {
                accepted = 1;
                break;
            }
        }

        /* NS not for us? */
        if (!accepted)
        {
            pbuf_free(p);
            return;
        }

        /* Check for ANY address in src (DAD algorithm). */
        if (ip6_addr_isany(ip6_current_src_addr()))
        {
            /* Sender is validating this address. */
            for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i)
            {
                if (!ip6_addr_isinvalid(netif_ip6_addr_state(inp, i))
                    && ip6_addr_cmp(&target_address, netif_ip6_addr(inp, i)))
                {
                    /* Send a NA back so that the sender does not use this address. */
                    nd6_send_na(inp, netif_ip6_addr(inp, i), ND6_FLAG_OVERRIDE | ND6_SEND_FLAG_ALLNODES_DEST);
                    if (ip6_addr_istentative(netif_ip6_addr_state(inp, i)))
                    {
                        /* We shouldn't use this address either. */
                        nd6_duplicate_addr_detected(inp, i);
                    }
                }
            }
        }
        else
        {
            /* Sender is trying to resolve our address. */
            /* Verify that they included their own link-layer address. */
            if (lladdr_opt == NULL)
            {
                /* Not a valid message. */
                pbuf_free(p);
                ND6_STATS_INC(nd6.proterr);
                ND6_STATS_INC(nd6.drop);
                return;
            }

            i = nd6_find_neighbor_cache_entry(ip6_current_src_addr());
            if (i >= 0)
            {
                /* We already have a record for the solicitor. */
                if (neighbor_cache[i].state == ND6_INCOMPLETE)
                {
                    neighbor_cache[i].netif = inp;
                    MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);

                    /* Delay probe in case we get confirmation of reachability from upper layer (TCP). */
                    neighbor_cache[i].state = ND6_DELAY;
                    neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME / ND6_TMR_INTERVAL;
                }
            }
            else
            {
                /* Add their IPv6 address and link-layer address to neighbor cache.
                 * We will need it at least to send a unicast NA message, but most
                 * likely we will also be communicating with this node soon. */
                i = nd6_new_neighbor_cache_entry();
                if (i < 0)
                {
                    /* We couldn't assign a cache entry for this neighbor.
                     * we won't be able to reply. drop it. */
                    pbuf_free(p);
                    ND6_STATS_INC(nd6.memerr);
                    return;
                }
                neighbor_cache[i].netif = inp;
                MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
                ip6_addr_set(&(neighbor_cache[i].next_hop_address), ip6_current_src_addr());

                /* Receiving a message does not prove reachability: only in one direction.
                 * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
                neighbor_cache[i].state = ND6_DELAY;
                neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME / ND6_TMR_INTERVAL;
            }

            /* Send back a NA for us. Allocate the reply pbuf. */
            nd6_send_na(inp, &target_address, ND6_FLAG_SOLICITED | ND6_FLAG_OVERRIDE);
        }

        break; /* ICMP6_TYPE_NS */
    }
    case ICMP6_TYPE_RA: /* Router Advertisement. */
    {
        struct ra_header* ra_hdr;
        u8_t* buffer; /* Used to copy options. */
        u16_t offset;
#if LWIP_ND6_RDNSS_MAX_DNS_SERVERS
        /* There can be multiple RDNSS options per RA */
        u8_t rdnss_server_idx = 0;
#endif /* LWIP_ND6_RDNSS_MAX_DNS_SERVERS */

        /* Check that RA header fits in packet. */
        if (p->len < sizeof(struct ra_header))
        {
            /* @todo debug message */
            pbuf_free(p);
            ND6_STATS_INC(nd6.lenerr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        ra_hdr = (struct ra_header*)p->payload;

        /* Check a subset of the other RFC 4861 Sec. 6.1.2 requirements. */
        if (!ip6_addr_islinklocal(ip6_current_src_addr()) || IP6H_HOPLIM(ip6_current_header()) != ND6_HOPLIM
            || ra_hdr->code != 0)
        {
            pbuf_free(p);
            ND6_STATS_INC(nd6.proterr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        /* @todo RFC MUST: all included options have a length greater than zero */

        /* If we are sending RS messages, stop. */
#if LWIP_IPV6_SEND_ROUTER_SOLICIT
        /* ensure at least one solicitation is sent (see RFC 4861, ch. 6.3.7) */
        if ((inp->rs_count < LWIP_ND6_MAX_MULTICAST_SOLICIT) || (nd6_send_rs(inp) == ERR_OK))
        {
            inp->rs_count = 0;
        }
        else
        {
            inp->rs_count = 1;
        }
#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */

        /* Get the matching default router entry. */
        i = nd6_get_router(ip6_current_src_addr(), inp);
        if (i < 0)
        {
            /* Create a new router entry. */
            i = nd6_new_router(ip6_current_src_addr(), inp);
        }

        if (i < 0)
        {
            /* Could not create a new router entry. */
            pbuf_free(p);
            ND6_STATS_INC(nd6.memerr);
            return;
        }

        /* Re-set invalidation timer. */
        default_router_list[i].invalidation_timer = lwip_htons(ra_hdr->router_lifetime);

        /* Re-set default timer values. */
#if LWIP_ND6_ALLOW_RA_UPDATES
        if (ra_hdr->retrans_timer > 0)
        {
            retrans_timer = lwip_htonl(ra_hdr->retrans_timer);
        }
        if (ra_hdr->reachable_time > 0)
        {
            reachable_time = lwip_htonl(ra_hdr->reachable_time);
        }
#endif /* LWIP_ND6_ALLOW_RA_UPDATES */

        /* @todo set default hop limit... */
        /* ra_hdr->current_hop_limit;*/

        /* Update flags in local entry (incl. preference). */
        default_router_list[i].flags = ra_hdr->flags;

#if LWIP_IPV6_DHCP6
        /* Trigger DHCPv6 if enabled */
        dhcp6_nd6_ra_trigger(
            inp,
            ra_hdr->flags & ND6_RA_FLAG_MANAGED_ADDR_CONFIG,
            ra_hdr->flags & ND6_RA_FLAG_OTHER_CONFIG);
#endif

        /* Offset to options. */
        offset = sizeof(struct ra_header);

        /* Process each option. */
        while ((p->tot_len - offset) >= 2)
        {
            u8_t option_type;
            u16_t option_len;
            int option_len8 = pbuf_try_get_at(p, offset + 1);
            if (option_len8 <= 0)
            {
                /* read beyond end or zero length */
                goto lenerr_drop_free_return;
            }
            option_len = ((u8_t)option_len8) << 3;
            if (option_len > p->tot_len - offset)
            {
                /* short packet (option does not fit in) */
                goto lenerr_drop_free_return;
            }
            if (p->len == p->tot_len)
            {
                /* no need to copy from contiguous pbuf */
                buffer = &((u8_t*)p->payload)[offset];
            }
            else
            {
                /* check if this option fits into our buffer */
                if (option_len > sizeof(nd6_ra_buffer))
                {
                    option_type = pbuf_get_at(p, offset);
                    /* invalid option length */
                    if (option_type != ND6_OPTION_TYPE_RDNSS)
                    {
                        goto lenerr_drop_free_return;
                    }
                    /* we allow RDNSS option to be longer - we'll just drop some servers */
                    option_len = sizeof(nd6_ra_buffer);
                }
                buffer = (u8_t*)&nd6_ra_buffer;
                option_len = pbuf_copy_partial(p, &nd6_ra_buffer, option_len, offset);
            }
            option_type = buffer[0];
            switch (option_type)
            {
            case ND6_OPTION_TYPE_SOURCE_LLADDR: {
                struct lladdr_option* lladdr_opt;
                if (option_len < sizeof(struct lladdr_option))
                {
                    goto lenerr_drop_free_return;
                }
                lladdr_opt = (struct lladdr_option*)buffer;
                if ((default_router_list[i].neighbor_entry != NULL)
                    && (default_router_list[i].neighbor_entry->state == ND6_INCOMPLETE))
                {
                    SMEMCPY(default_router_list[i].neighbor_entry->lladdr, lladdr_opt->addr, inp->hwaddr_len);
                    default_router_list[i].neighbor_entry->state = ND6_REACHABLE;
                    default_router_list[i].neighbor_entry->counter.reachable_time = reachable_time;
                }
                break;
            }
            case ND6_OPTION_TYPE_MTU: {
                struct mtu_option* mtu_opt;
                u32_t mtu32;
                if (option_len < sizeof(struct mtu_option))
                {
                    goto lenerr_drop_free_return;
                }
                mtu_opt = (struct mtu_option*)buffer;
                mtu32 = lwip_htonl(mtu_opt->mtu);
                if ((mtu32 >= 1280) && (mtu32 <= 0xffff))
                {
#if LWIP_ND6_ALLOW_RA_UPDATES
                    if (inp->mtu)
                    {
                        /* don't set the mtu for IPv6 higher than the netif driver supports */
                        inp->mtu6 = LWIP_MIN(inp->mtu, (u16_t)mtu32);
                    }
                    else
                    {
                        inp->mtu6 = (u16_t)mtu32;
                    }
#endif /* LWIP_ND6_ALLOW_RA_UPDATES */
                }
                break;
            }
            case ND6_OPTION_TYPE_PREFIX_INFO: {
                struct prefix_option* prefix_opt;
                ip6_addr_t prefix_addr;
                if (option_len < sizeof(struct prefix_option))
                {
                    goto lenerr_drop_free_return;
                }

                prefix_opt = (struct prefix_option*)buffer;

                /* Get a memory-aligned copy of the prefix. */
                ip6_addr_copy_from_packed(prefix_addr, prefix_opt->prefix);
                ip6_addr_assign_zone(&prefix_addr, IP6_UNICAST, inp);

                if (!ip6_addr_islinklocal(&prefix_addr))
                {
                    if ((prefix_opt->flags & ND6_PREFIX_FLAG_ON_LINK) && (prefix_opt->prefix_length == 64))
                    {
                        /* Add to on-link prefix list. */
                        u32_t valid_life;
                        s8_t prefix;

                        valid_life = lwip_htonl(prefix_opt->valid_lifetime);

                        /* find cache entry for this prefix. */
                        prefix = nd6_get_onlink_prefix(&prefix_addr, inp);
                        if (prefix < 0 && valid_life > 0)
                        {
                            /* Create a new cache entry. */
                            prefix = nd6_new_onlink_prefix(&prefix_addr, inp);
                        }
                        if (prefix >= 0)
                        {
                            prefix_list[prefix].invalidation_timer = valid_life;
                        }
                    }
#if LWIP_IPV6_AUTOCONFIG
                    if (prefix_opt->flags & ND6_PREFIX_FLAG_AUTONOMOUS)
                    {
                        /* Perform processing for autoconfiguration. */
                        nd6_process_autoconfig_prefix(inp, prefix_opt, &prefix_addr);
                    }
#endif /* LWIP_IPV6_AUTOCONFIG */
                }

                break;
            }
            case ND6_OPTION_TYPE_ROUTE_INFO:
                /* @todo implement preferred routes.
                struct route_option * route_opt;
                route_opt = (struct route_option *)buffer;*/

                break;
#if LWIP_ND6_RDNSS_MAX_DNS_SERVERS
            case ND6_OPTION_TYPE_RDNSS: {
                u8_t num, n;
                u16_t copy_offset = offset + SIZEOF_RDNSS_OPTION_BASE;
                struct rdnss_option* rdnss_opt;
                if (option_len < SIZEOF_RDNSS_OPTION_BASE)
                {
                    goto lenerr_drop_free_return;
                }

                rdnss_opt = (struct rdnss_option*)buffer;
                num = (rdnss_opt->length - 1) / 2;
                for (n = 0; (rdnss_server_idx < DNS_MAX_SERVERS) && (n < num); n++)
                {
                    ip_addr_t rdnss_address;

                    /* Copy directly from pbuf to get an aligned, zoned copy of the prefix. */
                    if (pbuf_copy_partial(p, &rdnss_address, sizeof(ip6_addr_p_t), copy_offset) == sizeof(ip6_addr_p_t))
                    {
                        IP_SET_TYPE_VAL(rdnss_address, IPADDR_TYPE_V6);
                        ip6_addr_assign_zone(ip_2_ip6(&rdnss_address), IP6_UNKNOWN, inp);

                        if (htonl(rdnss_opt->lifetime) > 0)
                        {
                            /* TODO implement Lifetime > 0 */
                            dns_setserver(rdnss_server_idx++, &rdnss_address);
                        }
                        else
                        {
                            /* TODO implement DNS removal in dns.c */
                            u8_t s;
                            for (s = 0; s < DNS_MAX_SERVERS; s++)
                            {
                                const ip_addr_t* addr = dns_getserver(s);
                                if (ip_addr_cmp(addr, &rdnss_address))
                                {
                                    dns_setserver(s, NULL);
                                }
                            }
                        }
                    }
                }
                break;
            }
#endif /* LWIP_ND6_RDNSS_MAX_DNS_SERVERS */
            default:
                /* Unrecognized option, abort. */
                ND6_STATS_INC(nd6.proterr);
                break;
            }
            /* option length is checked earlier to be non-zero to make sure loop ends */
            offset += 8 * (u8_t)option_len8;
        }

        break; /* ICMP6_TYPE_RA */
    }
    case ICMP6_TYPE_RD: /* Redirect */
    {
        struct redirect_header* redir_hdr;
        struct lladdr_option* lladdr_opt;
        ip6_addr_t destination_address, target_address;

        /* Check that Redir header fits in packet. */
        if (p->len < sizeof(struct redirect_header))
        {
            /* @todo debug message */
            pbuf_free(p);
            ND6_STATS_INC(nd6.lenerr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        redir_hdr = (struct redirect_header*)p->payload;

        /* Create an aligned, zoned copy of the destination address. */
        ip6_addr_copy_from_packed(destination_address, redir_hdr->destination_address);
        ip6_addr_assign_zone(&destination_address, IP6_UNICAST, inp);

        /* Check a subset of the other RFC 4861 Sec. 8.1 requirements. */
        if (!ip6_addr_islinklocal(ip6_current_src_addr()) || IP6H_HOPLIM(ip6_current_header()) != ND6_HOPLIM
            || redir_hdr->code != 0 || ip6_addr_ismulticast(&destination_address))
        {
            pbuf_free(p);
            ND6_STATS_INC(nd6.proterr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        /* @todo RFC MUST: IP source address equals first-hop router for destination_address */
        /* @todo RFC MUST: ICMP target address is either link-local address or same as destination_address */
        /* @todo RFC MUST: all included options have a length greater than zero */

        if (p->len >= (sizeof(struct redirect_header) + 2))
        {
            lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct redirect_header));
            if (p->len < (sizeof(struct redirect_header) + (lladdr_opt->length << 3)))
            {
                lladdr_opt = NULL;
            }
        }
        else
        {
            lladdr_opt = NULL;
        }

        /* Find dest address in cache */
        dest_idx = nd6_find_destination_cache_entry(&destination_address);
        if (dest_idx < 0)
        {
            /* Destination not in cache, drop packet. */
            pbuf_free(p);
            return;
        }

        /* Create an aligned, zoned copy of the target address. */
        ip6_addr_copy_from_packed(target_address, redir_hdr->target_address);
        ip6_addr_assign_zone(&target_address, IP6_UNICAST, inp);

        /* Set the new target address. */
        ip6_addr_copy(destination_cache[dest_idx].next_hop_addr, target_address);

        /* If Link-layer address of other router is given, try to add to neighbor cache. */
        if (lladdr_opt != NULL)
        {
            if (lladdr_opt->type == ND6_OPTION_TYPE_TARGET_LLADDR)
            {
                i = nd6_find_neighbor_cache_entry(&target_address);
                if (i < 0)
                {
                    i = nd6_new_neighbor_cache_entry();
                    if (i >= 0)
                    {
                        neighbor_cache[i].netif = inp;
                        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
                        ip6_addr_copy(neighbor_cache[i].next_hop_address, target_address);

                        /* Receiving a message does not prove reachability: only in one direction.
                         * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
                        neighbor_cache[i].state = ND6_DELAY;
                        neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME / ND6_TMR_INTERVAL;
                    }
                }
                if (i >= 0)
                {
                    if (neighbor_cache[i].state == ND6_INCOMPLETE)
                    {
                        MEMCPY(neighbor_cache[i].lladdr, lladdr_opt->addr, inp->hwaddr_len);
                        /* Receiving a message does not prove reachability: only in one direction.
                         * Delay probe in case we get confirmation of reachability from upper layer (TCP). */
                        neighbor_cache[i].state = ND6_DELAY;
                        neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME / ND6_TMR_INTERVAL;
                    }
                }
            }
        }
        break; /* ICMP6_TYPE_RD */
    }
    case ICMP6_TYPE_PTB: /* Packet too big */
    {
        struct icmp6_hdr* icmp6hdr; /* Packet too big message */
        struct ip6_hdr* ip6hdr;     /* IPv6 header of the packet which caused the error */
        u32_t pmtu;
        ip6_addr_t destination_address;

        /* Check that ICMPv6 header + IPv6 header fit in payload */
        if (p->len < (sizeof(struct icmp6_hdr) + IP6_HLEN))
        {
            /* drop short packets */
            pbuf_free(p);
            ND6_STATS_INC(nd6.lenerr);
            ND6_STATS_INC(nd6.drop);
            return;
        }

        icmp6hdr = (struct icmp6_hdr*)p->payload;
        ip6hdr = (struct ip6_hdr*)((u8_t*)p->payload + sizeof(struct icmp6_hdr));

        /* Create an aligned, zoned copy of the destination address. */
        ip6_addr_copy_from_packed(destination_address, ip6hdr->dest);
        ip6_addr_assign_zone(&destination_address, IP6_UNKNOWN, inp);

        /* Look for entry in destination cache. */
        dest_idx = nd6_find_destination_cache_entry(&destination_address);
        if (dest_idx < 0)
        {
            /* Destination not in cache, drop packet. */
            pbuf_free(p);
            return;
        }

        /* Change the Path MTU. */
        pmtu = lwip_htonl(icmp6hdr->data);
        destination_cache[dest_idx].pmtu = (u16_t)LWIP_MIN(pmtu, 0xFFFF);

        break; /* ICMP6_TYPE_PTB */
    }

    default:
        ND6_STATS_INC(nd6.proterr);
        ND6_STATS_INC(nd6.drop);
        break; /* default */
    }

    pbuf_free(p);
    return;
lenerr_drop_free_return:
    ND6_STATS_INC(nd6.lenerr);
    ND6_STATS_INC(nd6.drop);
    pbuf_free(p);
}

/**
 * Periodic timer for Neighbor discovery functions:
 *
 * - Update neighbor reachability states
 * - Update destination cache entries age
 * - Update invalidation timers of default routers and on-link prefixes
 * - Update lifetimes of our addresses
 * - Perform duplicate address detection (DAD) for our addresses
 * - Send router solicitations
 */
void nd6_tmr(void)
{
    s8_t i;
    struct netif* netif;

    /* Process neighbor entries. */
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        switch (neighbor_cache[i].state)
        {
        case ND6_INCOMPLETE:
            if ((neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT)
                && (!neighbor_cache[i].isrouter))
            {
                /* Retries exceeded. */
                nd6_free_neighbor_cache_entry(i);
            }
            else
            {
                /* Send a NS for this entry. */
                neighbor_cache[i].counter.probes_sent++;
                nd6_send_neighbor_cache_probe(&neighbor_cache[i], ND6_SEND_FLAG_MULTICAST_DEST);
            }
            break;
        case ND6_REACHABLE:
            /* Send queued packets, if any are left. Should have been sent already. */
            if (neighbor_cache[i].q != NULL)
            {
                nd6_send_q(i);
            }
            if (neighbor_cache[i].counter.reachable_time <= ND6_TMR_INTERVAL)
            {
                /* Change to stale state. */
                neighbor_cache[i].state = ND6_STALE;
                neighbor_cache[i].counter.stale_time = 0;
            }
            else
            {
                neighbor_cache[i].counter.reachable_time -= ND6_TMR_INTERVAL;
            }
            break;
        case ND6_STALE:
            neighbor_cache[i].counter.stale_time++;
            break;
        case ND6_DELAY:
            if (neighbor_cache[i].counter.delay_time <= 1)
            {
                /* Change to PROBE state. */
                neighbor_cache[i].state = ND6_PROBE;
                neighbor_cache[i].counter.probes_sent = 0;
            }
            else
            {
                neighbor_cache[i].counter.delay_time--;
            }
            break;
        case ND6_PROBE:
            if ((neighbor_cache[i].counter.probes_sent >= LWIP_ND6_MAX_MULTICAST_SOLICIT)
                && (!neighbor_cache[i].isrouter))
            {
                /* Retries exceeded. */
                nd6_free_neighbor_cache_entry(i);
            }
            else
            {
                /* Send a NS for this entry. */
                neighbor_cache[i].counter.probes_sent++;
                nd6_send_neighbor_cache_probe(&neighbor_cache[i], 0);
            }
            break;
        case ND6_NO_ENTRY:
        default:
            /* Do nothing. */
            break;
        }
    }

    /* Process destination entries. */
    for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++)
    {
        destination_cache[i].age++;
    }

    /* Process router entries. */
    for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++)
    {
        if (default_router_list[i].neighbor_entry != NULL)
        {
            /* Active entry. */
            if (default_router_list[i].invalidation_timer <= ND6_TMR_INTERVAL / 1000)
            {
                /* No more than 1 second remaining. Clear this entry. Also clear any of
                 * its destination cache entries, as per RFC 4861 Sec. 5.3 and 6.3.5. */
                s8_t j;
                for (j = 0; j < LWIP_ND6_NUM_DESTINATIONS; j++)
                {
                    if (ip6_addr_cmp(
                            &destination_cache[j].next_hop_addr,
                            &default_router_list[i].neighbor_entry->next_hop_address))
                    {
                        ip6_addr_set_any(&destination_cache[j].destination_addr);
                    }
                }
                default_router_list[i].neighbor_entry->isrouter = 0;
                default_router_list[i].neighbor_entry = NULL;
                default_router_list[i].invalidation_timer = 0;
                default_router_list[i].flags = 0;
            }
            else
            {
                default_router_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
            }
        }
    }

    /* Process prefix entries. */
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++)
    {
        if (prefix_list[i].netif != NULL)
        {
            if (prefix_list[i].invalidation_timer <= ND6_TMR_INTERVAL / 1000)
            {
                /* Entry timed out, remove it */
                prefix_list[i].invalidation_timer = 0;
                prefix_list[i].netif = NULL;
            }
            else
            {
                prefix_list[i].invalidation_timer -= ND6_TMR_INTERVAL / 1000;
            }
        }
    }

    /* Process our own addresses, updating address lifetimes and/or DAD state. */
    NETIF_FOREACH(netif)
    {
        for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i)
        {
            u8_t addr_state;
#if LWIP_IPV6_ADDRESS_LIFETIMES
            /* Step 1: update address lifetimes (valid and preferred). */
            addr_state = netif_ip6_addr_state(netif, i);
            /* RFC 4862 is not entirely clear as to whether address lifetimes affect
             * tentative addresses, and is even less clear as to what should happen
             * with duplicate addresses. We choose to track and update lifetimes for
             * both those types, although for different reasons:
             * - for tentative addresses, the line of thought of Sec. 5.7 combined
             *   with the potentially long period that an address may be in tentative
             *   state (due to the interface being down) suggests that lifetimes
             *   should be independent of external factors which would include DAD;
             * - for duplicate addresses, retiring them early could result in a new
             *   but unwanted attempt at marking them as valid, while retiring them
             *   late/never could clog up address slots on the netif.
             * As a result, we may end up expiring addresses of either type here.
             */
            if (!ip6_addr_isinvalid(addr_state) && !netif_ip6_addr_isstatic(netif, i))
            {
                u32_t life = netif_ip6_addr_valid_life(netif, i);
                if (life <= ND6_TMR_INTERVAL / 1000)
                {
                    /* The address has expired. */
                    netif_ip6_addr_set_valid_life(netif, i, 0);
                    netif_ip6_addr_set_pref_life(netif, i, 0);
                    netif_ip6_addr_set_state(netif, i, IP6_ADDR_INVALID);
                }
                else
                {
                    if (!ip6_addr_life_isinfinite(life))
                    {
                        life -= ND6_TMR_INTERVAL / 1000;
                        LWIP_ASSERT("bad valid lifetime", life != IP6_ADDR_LIFE_STATIC);
                        netif_ip6_addr_set_valid_life(netif, i, life);
                    }
                    /* The address is still here. Update the preferred lifetime too. */
                    life = netif_ip6_addr_pref_life(netif, i);
                    if (life <= ND6_TMR_INTERVAL / 1000)
                    {
                        /* This case must also trigger if 'life' was already zero, so as to
                         * deal correctly with advertised preferred-lifetime reductions. */
                        netif_ip6_addr_set_pref_life(netif, i, 0);
                        if (addr_state == IP6_ADDR_PREFERRED)
                            netif_ip6_addr_set_state(netif, i, IP6_ADDR_DEPRECATED);
                    }
                    else if (!ip6_addr_life_isinfinite(life))
                    {
                        life -= ND6_TMR_INTERVAL / 1000;
                        netif_ip6_addr_set_pref_life(netif, i, life);
                    }
                }
            }
            /* The address state may now have changed, so reobtain it next. */
#endif /* LWIP_IPV6_ADDRESS_LIFETIMES */
            /* Step 2: update DAD state. */
            addr_state = netif_ip6_addr_state(netif, i);
            if (ip6_addr_istentative(addr_state))
            {
                if ((addr_state & IP6_ADDR_TENTATIVE_COUNT_MASK) >= LWIP_IPV6_DUP_DETECT_ATTEMPTS)
                {
                    /* No NA received in response. Mark address as valid. For dynamic
                     * addresses with an expired preferred lifetime, the state is set to
                     * deprecated right away. That should almost never happen, though. */
                    addr_state = IP6_ADDR_PREFERRED;
#if LWIP_IPV6_ADDRESS_LIFETIMES
                    if (!netif_ip6_addr_isstatic(netif, i) && netif_ip6_addr_pref_life(netif, i) == 0)
                    {
                        addr_state = IP6_ADDR_DEPRECATED;
                    }
#endif /* LWIP_IPV6_ADDRESS_LIFETIMES */
                    netif_ip6_addr_set_state(netif, i, addr_state);
                }
                else if (netif_is_up(netif) && netif_is_link_up(netif))
                {
                    /* tentative: set next state by increasing by one */
                    netif_ip6_addr_set_state(netif, i, addr_state + 1);
                    /* Send a NS for this address. Use the unspecified address as source
                     * address in all cases (RFC 4862 Sec. 5.4.2), not in the least
                     * because as it is, we only consider multicast replies for DAD. */
                    nd6_send_ns(netif, netif_ip6_addr(netif, i), ND6_SEND_FLAG_MULTICAST_DEST | ND6_SEND_FLAG_ANY_SRC);
                }
            }
        }
    }

#if LWIP_IPV6_SEND_ROUTER_SOLICIT
    /* Send router solicitation messages, if necessary. */
    if (!nd6_tmr_rs_reduction)
    {
        nd6_tmr_rs_reduction = (ND6_RTR_SOLICITATION_INTERVAL / ND6_TMR_INTERVAL) - 1;
        NETIF_FOREACH(netif)
        {
            if ((netif->rs_count > 0) && netif_is_up(netif) && netif_is_link_up(netif)
                && !ip6_addr_isinvalid(netif_ip6_addr_state(netif, 0))
                && !ip6_addr_isduplicated(netif_ip6_addr_state(netif, 0)))
            {
                if (nd6_send_rs(netif) == ERR_OK)
                {
                    netif->rs_count--;
                }
            }
        }
    }
    else
    {
        nd6_tmr_rs_reduction--;
    }
#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
}

/** Send a neighbor solicitation message for a specific neighbor cache entry
 *
 * @param entry the neightbor cache entry for wich to send the message
 * @param flags one of ND6_SEND_FLAG_*
 */
static void nd6_send_neighbor_cache_probe(struct nd6_neighbor_cache_entry* entry, u8_t flags)
{
    nd6_send_ns(entry->netif, &entry->next_hop_address, flags);
}

/**
 * Send a neighbor solicitation message
 *
 * @param netif the netif on which to send the message
 * @param target_addr the IPv6 target address for the ND message
 * @param flags one of ND6_SEND_FLAG_*
 */
static void nd6_send_ns(struct netif* netif, const ip6_addr_t* target_addr, u8_t flags)
{
    struct ns_header* ns_hdr;
    struct pbuf* p;
    const ip6_addr_t* src_addr;
    u16_t lladdr_opt_len;

    LWIP_ASSERT("target address is required", target_addr != NULL);

    if (!(flags & ND6_SEND_FLAG_ANY_SRC) && ip6_addr_isvalid(netif_ip6_addr_state(netif, 0)))
    {
        /* Use link-local address as source address. */
        src_addr = netif_ip6_addr(netif, 0);
        /* calculate option length (in 8-byte-blocks) */
        lladdr_opt_len = ((netif->hwaddr_len + 2) + 7) >> 3;
    }
    else
    {
        src_addr = IP6_ADDR_ANY6;
        /* Option "MUST NOT be included when the source IP address is the unspecified address." */
        lladdr_opt_len = 0;
    }

    /* Allocate a packet. */
    p = pbuf_alloc(PBUF_IP, sizeof(struct ns_header) + (lladdr_opt_len << 3), PBUF_RAM);
    if (p == NULL)
    {
        ND6_STATS_INC(nd6.memerr);
        return;
    }

    /* Set fields. */
    ns_hdr = (struct ns_header*)p->payload;

    ns_hdr->type = ICMP6_TYPE_NS;
    ns_hdr->code = 0;
    ns_hdr->chksum = 0;
    ns_hdr->reserved = 0;
    ip6_addr_copy_to_packed(ns_hdr->target_address, *target_addr);

    if (lladdr_opt_len != 0)
    {
        struct lladdr_option* lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct ns_header));
        lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
        lladdr_opt->length = (u8_t)lladdr_opt_len;
        SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
    }

    /* Generate the solicited node address for the target address. */
    if (flags & ND6_SEND_FLAG_MULTICAST_DEST)
    {
        ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
        ip6_addr_assign_zone(&multicast_address, IP6_MULTICAST, netif);
        target_addr = &multicast_address;
    }

#if CHECKSUM_GEN_ICMP6
    IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_ICMP6)
    {
        ns_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr, target_addr);
    }
#endif /* CHECKSUM_GEN_ICMP6 */

    /* Send the packet out. */
    ND6_STATS_INC(nd6.xmit);
    ip6_output_if(p, (src_addr == IP6_ADDR_ANY6) ? NULL : src_addr, target_addr, ND6_HOPLIM, 0, IP6_NEXTH_ICMP6, netif);
    pbuf_free(p);
}

/**
 * Send a neighbor advertisement message
 *
 * @param netif the netif on which to send the message
 * @param target_addr the IPv6 target address for the ND message
 * @param flags one of ND6_SEND_FLAG_*
 */
static void nd6_send_na(struct netif* netif, const ip6_addr_t* target_addr, u8_t flags)
{
    struct na_header* na_hdr;
    struct lladdr_option* lladdr_opt;
    struct pbuf* p;
    const ip6_addr_t* src_addr;
    const ip6_addr_t* dest_addr;
    u16_t lladdr_opt_len;

    LWIP_ASSERT("target address is required", target_addr != NULL);

    /* Use link-local address as source address. */
    /* src_addr = netif_ip6_addr(netif, 0); */
    /* Use target address as source address. */
    src_addr = target_addr;

    /* Allocate a packet. */
    lladdr_opt_len = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
    p = pbuf_alloc(PBUF_IP, sizeof(struct na_header) + (lladdr_opt_len << 3), PBUF_RAM);
    if (p == NULL)
    {
        ND6_STATS_INC(nd6.memerr);
        return;
    }

    /* Set fields. */
    na_hdr = (struct na_header*)p->payload;
    lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct na_header));

    na_hdr->type = ICMP6_TYPE_NA;
    na_hdr->code = 0;
    na_hdr->chksum = 0;
    na_hdr->flags = flags & 0xf0;
    na_hdr->reserved[0] = 0;
    na_hdr->reserved[1] = 0;
    na_hdr->reserved[2] = 0;
    ip6_addr_copy_to_packed(na_hdr->target_address, *target_addr);

    lladdr_opt->type = ND6_OPTION_TYPE_TARGET_LLADDR;
    lladdr_opt->length = (u8_t)lladdr_opt_len;
    SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);

    /* Generate the solicited node address for the target address. */
    if (flags & ND6_SEND_FLAG_MULTICAST_DEST)
    {
        ip6_addr_set_solicitednode(&multicast_address, target_addr->addr[3]);
        ip6_addr_assign_zone(&multicast_address, IP6_MULTICAST, netif);
        dest_addr = &multicast_address;
    }
    else if (flags & ND6_SEND_FLAG_ALLNODES_DEST)
    {
        ip6_addr_set_allnodes_linklocal(&multicast_address);
        ip6_addr_assign_zone(&multicast_address, IP6_MULTICAST, netif);
        dest_addr = &multicast_address;
    }
    else
    {
        dest_addr = ip6_current_src_addr();
    }

#if CHECKSUM_GEN_ICMP6
    IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_ICMP6)
    {
        na_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr, dest_addr);
    }
#endif /* CHECKSUM_GEN_ICMP6 */

    /* Send the packet out. */
    ND6_STATS_INC(nd6.xmit);
    ip6_output_if(p, src_addr, dest_addr, ND6_HOPLIM, 0, IP6_NEXTH_ICMP6, netif);
    pbuf_free(p);
}

#if LWIP_IPV6_SEND_ROUTER_SOLICIT
/**
 * Send a router solicitation message
 *
 * @param netif the netif on which to send the message
 */
static err_t nd6_send_rs(struct netif* netif)
{
    struct rs_header* rs_hdr;
    struct lladdr_option* lladdr_opt;
    struct pbuf* p;
    const ip6_addr_t* src_addr;
    err_t err;
    u16_t lladdr_opt_len = 0;

    /* Link-local source address, or unspecified address? */
    if (ip6_addr_isvalid(netif_ip6_addr_state(netif, 0)))
    {
        src_addr = netif_ip6_addr(netif, 0);
    }
    else
    {
        src_addr = IP6_ADDR_ANY6;
    }

    /* Generate the all routers target address. */
    ip6_addr_set_allrouters_linklocal(&multicast_address);
    ip6_addr_assign_zone(&multicast_address, IP6_MULTICAST, netif);

    /* Allocate a packet. */
    if (src_addr != IP6_ADDR_ANY6)
    {
        lladdr_opt_len = ((netif->hwaddr_len + 2) >> 3) + (((netif->hwaddr_len + 2) & 0x07) ? 1 : 0);
    }
    p = pbuf_alloc(PBUF_IP, sizeof(struct rs_header) + (lladdr_opt_len << 3), PBUF_RAM);
    if (p == NULL)
    {
        ND6_STATS_INC(nd6.memerr);
        return ERR_BUF;
    }

    /* Set fields. */
    rs_hdr = (struct rs_header*)p->payload;

    rs_hdr->type = ICMP6_TYPE_RS;
    rs_hdr->code = 0;
    rs_hdr->chksum = 0;
    rs_hdr->reserved = 0;

    if (src_addr != IP6_ADDR_ANY6)
    {
        /* Include our hw address. */
        lladdr_opt = (struct lladdr_option*)((u8_t*)p->payload + sizeof(struct rs_header));
        lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
        lladdr_opt->length = (u8_t)lladdr_opt_len;
        SMEMCPY(lladdr_opt->addr, netif->hwaddr, netif->hwaddr_len);
    }

#if CHECKSUM_GEN_ICMP6
    IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_ICMP6)
    {
        rs_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len, src_addr, &multicast_address);
    }
#endif /* CHECKSUM_GEN_ICMP6 */

    /* Send the packet out. */
    ND6_STATS_INC(nd6.xmit);

    err = ip6_output_if(
        p,
        (src_addr == IP6_ADDR_ANY6) ? NULL : src_addr,
        &multicast_address,
        ND6_HOPLIM,
        0,
        IP6_NEXTH_ICMP6,
        netif);
    pbuf_free(p);

    return err;
}
#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */

/**
 * Search for a neighbor cache entry
 *
 * @param ip6addr the IPv6 address of the neighbor
 * @return The neighbor cache entry index that matched, -1 if no
 * entry is found
 */
static s8_t nd6_find_neighbor_cache_entry(const ip6_addr_t* ip6addr)
{
    s8_t i;
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if (ip6_addr_cmp(ip6addr, &(neighbor_cache[i].next_hop_address)))
        {
            return i;
        }
    }
    return -1;
}

/**
 * Create a new neighbor cache entry.
 *
 * If no unused entry is found, will try to recycle an old entry
 * according to ad-hoc "age" heuristic.
 *
 * @return The neighbor cache entry index that was created, -1 if no
 * entry could be created
 */
static s8_t nd6_new_neighbor_cache_entry(void)
{
    s8_t i;
    s8_t j;
    u32_t time;

    /* First, try to find an empty entry. */
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if (neighbor_cache[i].state == ND6_NO_ENTRY)
        {
            return i;
        }
    }

    /* We need to recycle an entry. in general, do not recycle if it is a router. */

    /* Next, try to find a Stale entry. */
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].state == ND6_STALE) && (!neighbor_cache[i].isrouter))
        {
            nd6_free_neighbor_cache_entry(i);
            return i;
        }
    }

    /* Next, try to find a Probe entry. */
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].state == ND6_PROBE) && (!neighbor_cache[i].isrouter))
        {
            nd6_free_neighbor_cache_entry(i);
            return i;
        }
    }

    /* Next, try to find a Delayed entry. */
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].state == ND6_DELAY) && (!neighbor_cache[i].isrouter))
        {
            nd6_free_neighbor_cache_entry(i);
            return i;
        }
    }

    /* Next, try to find the oldest reachable entry. */
    time = 0xfffffffful;
    j = -1;
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].state == ND6_REACHABLE) && (!neighbor_cache[i].isrouter))
        {
            if (neighbor_cache[i].counter.reachable_time < time)
            {
                j = i;
                time = neighbor_cache[i].counter.reachable_time;
            }
        }
    }
    if (j >= 0)
    {
        nd6_free_neighbor_cache_entry(j);
        return j;
    }

    /* Next, find oldest incomplete entry without queued packets. */
    time = 0;
    j = -1;
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].q == NULL) && (neighbor_cache[i].state == ND6_INCOMPLETE)
            && (!neighbor_cache[i].isrouter))
        {
            if (neighbor_cache[i].counter.probes_sent >= time)
            {
                j = i;
                time = neighbor_cache[i].counter.probes_sent;
            }
        }
    }
    if (j >= 0)
    {
        nd6_free_neighbor_cache_entry(j);
        return j;
    }

    /* Next, find oldest incomplete entry with queued packets. */
    time = 0;
    j = -1;
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if ((neighbor_cache[i].state == ND6_INCOMPLETE) && (!neighbor_cache[i].isrouter))
        {
            if (neighbor_cache[i].counter.probes_sent >= time)
            {
                j = i;
                time = neighbor_cache[i].counter.probes_sent;
            }
        }
    }
    if (j >= 0)
    {
        nd6_free_neighbor_cache_entry(j);
        return j;
    }

    /* No more entries to try. */
    return -1;
}

/**
 * Will free any resources associated with a neighbor cache
 * entry, and will mark it as unused.
 *
 * @param i the neighbor cache entry index to free
 */
static void nd6_free_neighbor_cache_entry(s8_t i)
{
    if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS))
    {
        return;
    }
    if (neighbor_cache[i].isrouter)
    {
        /* isrouter needs to be cleared before deleting a neighbor cache entry */
        return;
    }

    /* Free any queued packets. */
    if (neighbor_cache[i].q != NULL)
    {
        nd6_free_q(neighbor_cache[i].q);
        neighbor_cache[i].q = NULL;
    }

    neighbor_cache[i].state = ND6_NO_ENTRY;
    neighbor_cache[i].isrouter = 0;
    neighbor_cache[i].netif = NULL;
    neighbor_cache[i].counter.reachable_time = 0;
    ip6_addr_set_zero(&(neighbor_cache[i].next_hop_address));
}

/**
 * Search for a destination cache entry
 *
 * @param ip6addr the IPv6 address of the destination
 * @return The destination cache entry index that matched, -1 if no
 * entry is found
 */
static s16_t nd6_find_destination_cache_entry(const ip6_addr_t* ip6addr)
{
    s16_t i;

    IP6_ADDR_ZONECHECK(ip6addr);

    for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++)
    {
        if (ip6_addr_cmp(ip6addr, &(destination_cache[i].destination_addr)))
        {
            return i;
        }
    }
    return -1;
}

/**
 * Create a new destination cache entry. If no unused entry is found,
 * will recycle oldest entry.
 *
 * @return The destination cache entry index that was created, -1 if no
 * entry was created
 */
static s16_t nd6_new_destination_cache_entry(void)
{
    s16_t i, j;
    u32_t age;

    /* Find an empty entry. */
    for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++)
    {
        if (ip6_addr_isany(&(destination_cache[i].destination_addr)))
        {
            return i;
        }
    }

    /* Find oldest entry. */
    age = 0;
    j = LWIP_ND6_NUM_DESTINATIONS - 1;
    for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++)
    {
        if (destination_cache[i].age > age)
        {
            j = i;
        }
    }

    return j;
}

/**
 * Clear the destination cache.
 *
 * This operation may be necessary for consistency in the light of changing
 * local addresses and/or use of the gateway hook.
 */
void nd6_clear_destination_cache(void)
{
    int i;

    for (i = 0; i < LWIP_ND6_NUM_DESTINATIONS; i++)
    {
        ip6_addr_set_any(&destination_cache[i].destination_addr);
    }
}

/**
 * Determine whether an address matches an on-link prefix or the subnet of a
 * statically assigned address.
 *
 * @param ip6addr the IPv6 address to match
 * @return 1 if the address is on-link, 0 otherwise
 */
static int nd6_is_prefix_in_netif(const ip6_addr_t* ip6addr, struct netif* netif)
{
    s8_t i;

    /* Check to see if the address matches an on-link prefix. */
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++)
    {
        if ((prefix_list[i].netif == netif) && (prefix_list[i].invalidation_timer > 0)
            && ip6_addr_netcmp(ip6addr, &(prefix_list[i].prefix)))
        {
            return 1;
        }
    }
    /* Check to see if address prefix matches a manually configured (= static)
     * address. Static addresses have an implied /64 subnet assignment. Dynamic
     * addresses (from autoconfiguration) have no implied subnet assignment, and
     * are thus effectively /128 assignments. See RFC 5942 for more on this. */
    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++)
    {
        if (ip6_addr_isvalid(netif_ip6_addr_state(netif, i)) && netif_ip6_addr_isstatic(netif, i)
            && ip6_addr_netcmp(ip6addr, netif_ip6_addr(netif, i)))
        {
            return 1;
        }
    }
    return 0;
}

/**
 * Select a default router for a destination.
 *
 * This function is used both for routing and for finding a next-hop target for
 * a packet. In the former case, the given netif is NULL, and the returned
 * router entry must be for a netif suitable for sending packets (up, link up).
 * In the latter case, the given netif is not NULL and restricts router choice.
 *
 * @param ip6addr the destination address
 * @param netif the netif for the outgoing packet, if known
 * @return the default router entry index, or -1 if no suitable
 *         router is found
 */
static s8_t nd6_select_router(const ip6_addr_t* ip6addr, struct netif* netif)
{
    struct netif* router_netif;
    s8_t i, j, valid_router;
    static s8_t last_router;

    LWIP_UNUSED_ARG(ip6addr); /* @todo match preferred routes!! (must implement ND6_OPTION_TYPE_ROUTE_INFO) */

    /* @todo: implement default router preference */

    /* Look for valid routers. A reachable router is preferred. */
    valid_router = -1;
    for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++)
    {
        /* Is the router netif both set and apppropriate? */
        if (default_router_list[i].neighbor_entry != NULL)
        {
            router_netif = default_router_list[i].neighbor_entry->netif;
            if ((router_netif != NULL)
                && (netif != NULL ? netif == router_netif
                                  : (netif_is_up(router_netif) && netif_is_link_up(router_netif))))
            {
                /* Is the router valid, i.e., reachable or probably reachable as per
                 * RFC 4861 Sec. 6.3.6? Note that we will never return a router that
                 * has no neighbor cache entry, due to the netif association tests. */
                if (default_router_list[i].neighbor_entry->state != ND6_INCOMPLETE)
                {
                    /* Is the router known to be reachable? */
                    if (default_router_list[i].neighbor_entry->state == ND6_REACHABLE)
                    {
                        return i; /* valid and reachable - done! */
                    }
                    else if (valid_router < 0)
                    {
                        valid_router = i; /* valid but not known to be reachable */
                    }
                }
            }
        }
    }
    if (valid_router >= 0)
    {
        return valid_router;
    }

    /* Look for any router for which we have any information at all. */
    /* last_router is used for round-robin selection of incomplete routers, as
     * recommended in RFC 4861 Sec. 6.3.6 point (2). Advance only when picking a
     * route, to select the same router as next-hop target in the common case. */
    if ((netif == NULL) && (++last_router >= LWIP_ND6_NUM_ROUTERS))
    {
        last_router = 0;
    }
    i = last_router;
    for (j = 0; j < LWIP_ND6_NUM_ROUTERS; j++)
    {
        if (default_router_list[i].neighbor_entry != NULL)
        {
            router_netif = default_router_list[i].neighbor_entry->netif;
            if ((router_netif != NULL)
                && (netif != NULL ? netif == router_netif
                                  : (netif_is_up(router_netif) && netif_is_link_up(router_netif))))
            {
                return i;
            }
        }
        if (++i >= LWIP_ND6_NUM_ROUTERS)
        {
            i = 0;
        }
    }

    /* no suitable router found. */
    return -1;
}

/**
 * Find a router-announced route to the given destination. This route may be
 * based on an on-link prefix or a default router.
 *
 * If a suitable route is found, the returned netif is guaranteed to be in a
 * suitable state (up, link up) to be used for packet transmission.
 *
 * @param ip6addr the destination IPv6 address
 * @return the netif to use for the destination, or NULL if none found
 */
struct netif* nd6_find_route(const ip6_addr_t* ip6addr)
{
    struct netif* netif;
    s8_t i;

    /* @todo decide if it makes sense to check the destination cache first */

    /* Check if there is a matching on-link prefix. There may be multiple
     * matches. Pick the first one that is associated with a suitable netif. */
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i)
    {
        netif = prefix_list[i].netif;
        if ((netif != NULL) && ip6_addr_netcmp(&prefix_list[i].prefix, ip6addr) && netif_is_up(netif)
            && netif_is_link_up(netif))
        {
            return netif;
        }
    }

    /* No on-link prefix match. Find a router that can forward the packet. */
    i = nd6_select_router(ip6addr, NULL);
    if (i >= 0)
    {
        LWIP_ASSERT("selected router must have a neighbor entry", default_router_list[i].neighbor_entry != NULL);
        return default_router_list[i].neighbor_entry->netif;
    }

    return NULL;
}

/**
 * Find an entry for a default router.
 *
 * @param router_addr the IPv6 address of the router
 * @param netif the netif on which the router is found, if known
 * @return the index of the router entry, or -1 if not found
 */
static s8_t nd6_get_router(const ip6_addr_t* router_addr, struct netif* netif)
{
    s8_t i;

    IP6_ADDR_ZONECHECK_NETIF(router_addr, netif);

    /* Look for router. */
    for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++)
    {
        if ((default_router_list[i].neighbor_entry != NULL)
            && ((netif != NULL) ? netif == default_router_list[i].neighbor_entry->netif : 1)
            && ip6_addr_cmp(router_addr, &(default_router_list[i].neighbor_entry->next_hop_address)))
        {
            return i;
        }
    }

    /* router not found. */
    return -1;
}

/**
 * Create a new entry for a default router.
 *
 * @param router_addr the IPv6 address of the router
 * @param netif the netif on which the router is connected, if known
 * @return the index on the router table, or -1 if could not be created
 */
static s8_t nd6_new_router(const ip6_addr_t* router_addr, struct netif* netif)
{
    s8_t router_index;
    s8_t free_router_index;
    s8_t neighbor_index;

    IP6_ADDR_ZONECHECK_NETIF(router_addr, netif);

    /* Do we have a neighbor entry for this router? */
    neighbor_index = nd6_find_neighbor_cache_entry(router_addr);
    if (neighbor_index < 0)
    {
        /* Create a neighbor entry for this router. */
        neighbor_index = nd6_new_neighbor_cache_entry();
        if (neighbor_index < 0)
        {
            /* Could not create neighbor entry for this router. */
            return -1;
        }
        ip6_addr_set(&(neighbor_cache[neighbor_index].next_hop_address), router_addr);
        neighbor_cache[neighbor_index].netif = netif;
        neighbor_cache[neighbor_index].q = NULL;
        neighbor_cache[neighbor_index].state = ND6_INCOMPLETE;
        neighbor_cache[neighbor_index].counter.probes_sent = 1;
        nd6_send_neighbor_cache_probe(&neighbor_cache[neighbor_index], ND6_SEND_FLAG_MULTICAST_DEST);
    }

    /* Mark neighbor as router. */
    neighbor_cache[neighbor_index].isrouter = 1;

    /* Look for empty entry. */
    free_router_index = LWIP_ND6_NUM_ROUTERS;
    for (router_index = LWIP_ND6_NUM_ROUTERS - 1; router_index >= 0; router_index--)
    {
        /* check if router already exists (this is a special case for 2 netifs on the same subnet
           - e.g. wifi and cable) */
        if (default_router_list[router_index].neighbor_entry == &(neighbor_cache[neighbor_index]))
        {
            return router_index;
        }
        if (default_router_list[router_index].neighbor_entry == NULL)
        {
            /* remember lowest free index to create a new entry */
            free_router_index = router_index;
        }
    }
    if (free_router_index < LWIP_ND6_NUM_ROUTERS)
    {
        default_router_list[free_router_index].neighbor_entry = &(neighbor_cache[neighbor_index]);
        return free_router_index;
    }

    /* Could not create a router entry. */

    /* Mark neighbor entry as not-router. Entry might be useful as neighbor still. */
    neighbor_cache[neighbor_index].isrouter = 0;

    /* router not found. */
    return -1;
}

/**
 * Find the cached entry for an on-link prefix.
 *
 * @param prefix the IPv6 prefix that is on-link
 * @param netif the netif on which the prefix is on-link
 * @return the index on the prefix table, or -1 if not found
 */
static s8_t nd6_get_onlink_prefix(const ip6_addr_t* prefix, struct netif* netif)
{
    s8_t i;

    /* Look for prefix in list. */
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i)
    {
        if ((ip6_addr_netcmp(&(prefix_list[i].prefix), prefix)) && (prefix_list[i].netif == netif))
        {
            return i;
        }
    }

    /* Entry not available. */
    return -1;
}

/**
 * Creates a new entry for an on-link prefix.
 *
 * @param prefix the IPv6 prefix that is on-link
 * @param netif the netif on which the prefix is on-link
 * @return the index on the prefix table, or -1 if not created
 */
static s8_t nd6_new_onlink_prefix(const ip6_addr_t* prefix, struct netif* netif)
{
    s8_t i;

    /* Create new entry. */
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; ++i)
    {
        if ((prefix_list[i].netif == NULL) || (prefix_list[i].invalidation_timer == 0))
        {
            /* Found empty prefix entry. */
            prefix_list[i].netif = netif;
            ip6_addr_set(&(prefix_list[i].prefix), prefix);
            return i;
        }
    }

    /* Entry not available. */
    return -1;
}

/**
 * Determine the next hop for a destination. Will determine if the
 * destination is on-link, else a suitable on-link router is selected.
 *
 * The last entry index is cached for fast entry search.
 *
 * @param ip6addr the destination address
 * @param netif the netif on which the packet will be sent
 * @return the neighbor cache entry for the next hop, ERR_RTE if no
 *         suitable next hop was found, ERR_MEM if no cache entry
 *         could be created
 */
static s8_t nd6_get_next_hop_entry(const ip6_addr_t* ip6addr, struct netif* netif)
{
#ifdef LWIP_HOOK_ND6_GET_GW
    const ip6_addr_t* next_hop_addr;
#endif /* LWIP_HOOK_ND6_GET_GW */
    s8_t i;
    s16_t dst_idx;

    IP6_ADDR_ZONECHECK_NETIF(ip6addr, netif);

#if LWIP_NETIF_HWADDRHINT
    if (netif->hints != NULL)
    {
        /* per-pcb cached entry was given */
        netif_addr_idx_t addr_hint = netif->hints->addr_hint;
        if (addr_hint < LWIP_ND6_NUM_DESTINATIONS)
        {
            nd6_cached_destination_index = addr_hint;
        }
    }
#endif /* LWIP_NETIF_HWADDRHINT */

    /* Look for ip6addr in destination cache. */
    if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr)))
    {
        /* the cached entry index is the right one! */
        /* do nothing. */
        ND6_STATS_INC(nd6.cachehit);
    }
    else
    {
        /* Search destination cache. */
        dst_idx = nd6_find_destination_cache_entry(ip6addr);
        if (dst_idx >= 0)
        {
            /* found destination entry. make it our new cached index. */
            LWIP_ASSERT("type overflow", (size_t)dst_idx < NETIF_ADDR_IDX_MAX);
            nd6_cached_destination_index = (netif_addr_idx_t)dst_idx;
        }
        else
        {
            /* Not found. Create a new destination entry. */
            dst_idx = nd6_new_destination_cache_entry();
            if (dst_idx >= 0)
            {
                /* got new destination entry. make it our new cached index. */
                LWIP_ASSERT("type overflow", (size_t)dst_idx < NETIF_ADDR_IDX_MAX);
                nd6_cached_destination_index = (netif_addr_idx_t)dst_idx;
            }
            else
            {
                /* Could not create a destination cache entry. */
                return ERR_MEM;
            }

            /* Copy dest address to destination cache. */
            ip6_addr_set(&(destination_cache[nd6_cached_destination_index].destination_addr), ip6addr);

            /* Now find the next hop. is it a neighbor? */
            if (ip6_addr_islinklocal(ip6addr) || nd6_is_prefix_in_netif(ip6addr, netif))
            {
                /* Destination in local link. */
                destination_cache[nd6_cached_destination_index].pmtu = netif_mtu6(netif);
                ip6_addr_copy(
                    destination_cache[nd6_cached_destination_index].next_hop_addr,
                    destination_cache[nd6_cached_destination_index].destination_addr);
#ifdef LWIP_HOOK_ND6_GET_GW
            }
            else if ((next_hop_addr = LWIP_HOOK_ND6_GET_GW(netif, ip6addr)) != NULL)
            {
                /* Next hop for destination provided by hook function. */
                destination_cache[nd6_cached_destination_index].pmtu = netif->mtu;
                ip6_addr_set(&destination_cache[nd6_cached_destination_index].next_hop_addr, next_hop_addr);
#endif /* LWIP_HOOK_ND6_GET_GW */
            }
            else
            {
                /* We need to select a router. */
                i = nd6_select_router(ip6addr, netif);
                if (i < 0)
                {
                    /* No router found. */
                    ip6_addr_set_any(&(destination_cache[nd6_cached_destination_index].destination_addr));
                    return ERR_RTE;
                }
                destination_cache[nd6_cached_destination_index].pmtu =
                    netif_mtu6(netif); /* Start with netif mtu, correct through ICMPv6 if necessary */
                ip6_addr_copy(
                    destination_cache[nd6_cached_destination_index].next_hop_addr,
                    default_router_list[i].neighbor_entry->next_hop_address);
            }
        }
    }

#if LWIP_NETIF_HWADDRHINT
    if (netif->hints != NULL)
    {
        /* per-pcb cached entry was given */
        netif->hints->addr_hint = nd6_cached_destination_index;
    }
#endif /* LWIP_NETIF_HWADDRHINT */

    /* Look in neighbor cache for the next-hop address. */
    if (ip6_addr_cmp(
            &(destination_cache[nd6_cached_destination_index].next_hop_addr),
            &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address)))
    {
        /* Cache hit. */
        /* Do nothing. */
        ND6_STATS_INC(nd6.cachehit);
    }
    else
    {
        i = nd6_find_neighbor_cache_entry(&(destination_cache[nd6_cached_destination_index].next_hop_addr));
        if (i >= 0)
        {
            /* Found a matching record, make it new cached entry. */
            nd6_cached_neighbor_index = i;
        }
        else
        {
            /* Neighbor not in cache. Make a new entry. */
            i = nd6_new_neighbor_cache_entry();
            if (i >= 0)
            {
                /* got new neighbor entry. make it our new cached index. */
                nd6_cached_neighbor_index = i;
            }
            else
            {
                /* Could not create a neighbor cache entry. */
                return ERR_MEM;
            }

            /* Initialize fields. */
            ip6_addr_copy(
                neighbor_cache[i].next_hop_address,
                destination_cache[nd6_cached_destination_index].next_hop_addr);
            neighbor_cache[i].isrouter = 0;
            neighbor_cache[i].netif = netif;
            neighbor_cache[i].state = ND6_INCOMPLETE;
            neighbor_cache[i].counter.probes_sent = 1;
            nd6_send_neighbor_cache_probe(&neighbor_cache[i], ND6_SEND_FLAG_MULTICAST_DEST);
        }
    }

    /* Reset this destination's age. */
    destination_cache[nd6_cached_destination_index].age = 0;

    return nd6_cached_neighbor_index;
}

/**
 * Queue a packet for a neighbor.
 *
 * @param neighbor_index the index in the neighbor cache table
 * @param q packet to be queued
 * @return ERR_OK if succeeded, ERR_MEM if out of memory
 */
static err_t nd6_queue_packet(s8_t neighbor_index, struct pbuf* q)
{
    err_t result = ERR_MEM;
    struct pbuf* p;
    int copy_needed = 0;
#if LWIP_ND6_QUEUEING
    struct nd6_q_entry *new_entry, *r;
#endif /* LWIP_ND6_QUEUEING */

    if ((neighbor_index < 0) || (neighbor_index >= LWIP_ND6_NUM_NEIGHBORS))
    {
        return ERR_ARG;
    }

    /* IF q includes a pbuf that must be copied, we have to copy the whole chain
     * into a new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
    p = q;
    while (p)
    {
        if (PBUF_NEEDS_COPY(p))
        {
            copy_needed = 1;
            break;
        }
        p = p->next;
    }
    if (copy_needed)
    {
        /* copy the whole packet into new pbufs */
        p = pbuf_clone(PBUF_LINK, PBUF_RAM, q);
        while ((p == NULL) && (neighbor_cache[neighbor_index].q != NULL))
        {
            /* Free oldest packet (as per RFC recommendation) */
#if LWIP_ND6_QUEUEING
            r = neighbor_cache[neighbor_index].q;
            neighbor_cache[neighbor_index].q = r->next;
            r->next = NULL;
            nd6_free_q(r);
#else  /* LWIP_ND6_QUEUEING */
            pbuf_free(neighbor_cache[neighbor_index].q);
            neighbor_cache[neighbor_index].q = NULL;
#endif /* LWIP_ND6_QUEUEING */
            p = pbuf_clone(PBUF_LINK, PBUF_RAM, q);
        }
    }
    else
    {
        /* referencing the old pbuf is enough */
        p = q;
        pbuf_ref(p);
    }
    /* packet was copied/ref'd? */
    if (p != NULL)
    {
        /* queue packet ... */
#if LWIP_ND6_QUEUEING
        /* allocate a new nd6 queue entry */
        new_entry = (struct nd6_q_entry*)memp_malloc(MEMP_ND6_QUEUE);
        if ((new_entry == NULL) && (neighbor_cache[neighbor_index].q != NULL))
        {
            /* Free oldest packet (as per RFC recommendation) */
            r = neighbor_cache[neighbor_index].q;
            neighbor_cache[neighbor_index].q = r->next;
            r->next = NULL;
            nd6_free_q(r);
            new_entry = (struct nd6_q_entry*)memp_malloc(MEMP_ND6_QUEUE);
        }
        if (new_entry != NULL)
        {
            new_entry->next = NULL;
            new_entry->p = p;
            if (neighbor_cache[neighbor_index].q != NULL)
            {
                /* queue was already existent, append the new entry to the end */
                r = neighbor_cache[neighbor_index].q;
                while (r->next != NULL)
                {
                    r = r->next;
                }
                r->next = new_entry;
            }
            else
            {
                /* queue did not exist, first item in queue */
                neighbor_cache[neighbor_index].q = new_entry;
            }
            LWIP_DEBUGF(
                LWIP_DBG_TRACE,
                ("ipv6: queued packet %p on neighbor entry %" S16_F "\n", (void*)p, (s16_t)neighbor_index));
            result = ERR_OK;
        }
        else
        {
            /* the pool MEMP_ND6_QUEUE is empty */
            pbuf_free(p);
            LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void*)p));
            /* { result == ERR_MEM } through initialization */
        }
#else  /* LWIP_ND6_QUEUEING */
        /* Queue a single packet. If an older packet is already queued, free it as per RFC. */
        if (neighbor_cache[neighbor_index].q != NULL)
        {
            pbuf_free(neighbor_cache[neighbor_index].q);
        }
        neighbor_cache[neighbor_index].q = p;
        LWIP_DEBUGF(
            LWIP_DBG_TRACE,
            ("ipv6: queued packet %p on neighbor entry %" S16_F "\n", (void*)p, (s16_t)neighbor_index));
        result = ERR_OK;
#endif /* LWIP_ND6_QUEUEING */
    }
    else
    {
        LWIP_DEBUGF(LWIP_DBG_TRACE, ("ipv6: could not queue a copy of packet %p (out of memory)\n", (void*)q));
        /* { result == ERR_MEM } through initialization */
    }

    return result;
}

#if LWIP_ND6_QUEUEING
/**
 * Free a complete queue of nd6 q entries
 *
 * @param q a queue of nd6_q_entry to free
 */
static void nd6_free_q(struct nd6_q_entry* q)
{
    struct nd6_q_entry* r;
    LWIP_ASSERT("q != NULL", q != NULL);
    LWIP_ASSERT("q->p != NULL", q->p != NULL);
    while (q)
    {
        r = q;
        q = q->next;
        LWIP_ASSERT("r->p != NULL", (r->p != NULL));
        pbuf_free(r->p);
        memp_free(MEMP_ND6_QUEUE, r);
    }
}
#endif /* LWIP_ND6_QUEUEING */

/**
 * Send queued packets for a neighbor
 *
 * @param i the neighbor to send packets to
 */
static void nd6_send_q(s8_t i)
{
    struct ip6_hdr* ip6hdr;
    ip6_addr_t dest;
#if LWIP_ND6_QUEUEING
    struct nd6_q_entry* q;
#endif /* LWIP_ND6_QUEUEING */

    if ((i < 0) || (i >= LWIP_ND6_NUM_NEIGHBORS))
    {
        return;
    }

#if LWIP_ND6_QUEUEING
    while (neighbor_cache[i].q != NULL)
    {
        /* remember first in queue */
        q = neighbor_cache[i].q;
        /* pop first item off the queue */
        neighbor_cache[i].q = q->next;
        /* Get ipv6 header. */
        ip6hdr = (struct ip6_hdr*)(q->p->payload);
        /* Create an aligned copy. */
        ip6_addr_copy_from_packed(dest, ip6hdr->dest);
        /* Restore the zone, if applicable. */
        ip6_addr_assign_zone(&dest, IP6_UNKNOWN, neighbor_cache[i].netif);
        /* send the queued IPv6 packet */
        (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, q->p, &dest);
        /* free the queued IP packet */
        pbuf_free(q->p);
        /* now queue entry can be freed */
        memp_free(MEMP_ND6_QUEUE, q);
    }
#else  /* LWIP_ND6_QUEUEING */
    if (neighbor_cache[i].q != NULL)
    {
        /* Get ipv6 header. */
        ip6hdr = (struct ip6_hdr*)(neighbor_cache[i].q->payload);
        /* Create an aligned copy. */
        ip6_addr_copy_from_packed(dest, ip6hdr->dest);
        /* Restore the zone, if applicable. */
        ip6_addr_assign_zone(&dest, IP6_UNKNOWN, neighbor_cache[i].netif);
        /* send the queued IPv6 packet */
        (neighbor_cache[i].netif)->output_ip6(neighbor_cache[i].netif, neighbor_cache[i].q, &dest);
        /* free the queued IP packet */
        pbuf_free(neighbor_cache[i].q);
        neighbor_cache[i].q = NULL;
    }
#endif /* LWIP_ND6_QUEUEING */
}

/**
 * A packet is to be transmitted to a specific IPv6 destination on a specific
 * interface. Check if we can find the hardware address of the next hop to use
 * for the packet. If so, give the hardware address to the caller, which should
 * use it to send the packet right away. Otherwise, enqueue the packet for
 * later transmission while looking up the hardware address, if possible.
 *
 * As such, this function returns one of three different possible results:
 *
 * - ERR_OK with a non-NULL 'hwaddrp': the caller should send the packet now.
 * - ERR_OK with a NULL 'hwaddrp': the packet has been enqueued for later.
 * - not ERR_OK: something went wrong; forward the error upward in the stack.
 *
 * @param netif The lwIP network interface on which the IP packet will be sent.
 * @param q The pbuf(s) containing the IP packet to be sent.
 * @param ip6addr The destination IPv6 address of the packet.
 * @param hwaddrp On success, filled with a pointer to a HW address or NULL (meaning
 *        the packet has been queued).
 * @return
 * - ERR_OK on success, ERR_RTE if no route was found for the packet,
 * or ERR_MEM if low memory conditions prohibit sending the packet at all.
 */
err_t nd6_get_next_hop_addr_or_queue(
    struct netif* netif,
    struct pbuf* q,
    const ip6_addr_t* ip6addr,
    const u8_t** hwaddrp)
{
    s8_t i;

    /* Get next hop record. */
    i = nd6_get_next_hop_entry(ip6addr, netif);
    if (i < 0)
    {
        /* failed to get a next hop neighbor record. */
        return i;
    }

    /* Now that we have a destination record, send or queue the packet. */
    if (neighbor_cache[i].state == ND6_STALE)
    {
        /* Switch to delay state. */
        neighbor_cache[i].state = ND6_DELAY;
        neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME / ND6_TMR_INTERVAL;
    }
    /* @todo should we send or queue if PROBE? send for now, to let unicast NS pass. */
    if ((neighbor_cache[i].state == ND6_REACHABLE) || (neighbor_cache[i].state == ND6_DELAY)
        || (neighbor_cache[i].state == ND6_PROBE))
    {

        /* Tell the caller to send out the packet now. */
        *hwaddrp = neighbor_cache[i].lladdr;
        return ERR_OK;
    }

    /* We should queue packet on this interface. */
    *hwaddrp = NULL;
    return nd6_queue_packet(i, q);
}

/**
 * Get the Path MTU for a destination.
 *
 * @param ip6addr the destination address
 * @param netif the netif on which the packet will be sent
 * @return the Path MTU, if known, or the netif default MTU
 */
u16_t nd6_get_destination_mtu(const ip6_addr_t* ip6addr, struct netif* netif)
{
    s16_t i;

    i = nd6_find_destination_cache_entry(ip6addr);
    if (i >= 0)
    {
        if (destination_cache[i].pmtu > 0)
        {
            return destination_cache[i].pmtu;
        }
    }

    if (netif != NULL)
    {
        return netif_mtu6(netif);
    }

    return 1280; /* Minimum MTU */
}

#if LWIP_ND6_TCP_REACHABILITY_HINTS
/**
 * Provide the Neighbor discovery process with a hint that a
 * destination is reachable. Called by tcp_receive when ACKs are
 * received or sent (as per RFC). This is useful to avoid sending
 * NS messages every 30 seconds.
 *
 * @param ip6addr the destination address which is know to be reachable
 *                by an upper layer protocol (TCP)
 */
void nd6_reachability_hint(const ip6_addr_t* ip6addr)
{
    s8_t i;
    s16_t dst_idx;

    /* Find destination in cache. */
    if (ip6_addr_cmp(ip6addr, &(destination_cache[nd6_cached_destination_index].destination_addr)))
    {
        dst_idx = nd6_cached_destination_index;
        ND6_STATS_INC(nd6.cachehit);
    }
    else
    {
        dst_idx = nd6_find_destination_cache_entry(ip6addr);
    }
    if (dst_idx < 0)
    {
        return;
    }

    /* Find next hop neighbor in cache. */
    if (ip6_addr_cmp(
            &(destination_cache[dst_idx].next_hop_addr),
            &(neighbor_cache[nd6_cached_neighbor_index].next_hop_address)))
    {
        i = nd6_cached_neighbor_index;
        ND6_STATS_INC(nd6.cachehit);
    }
    else
    {
        i = nd6_find_neighbor_cache_entry(&(destination_cache[dst_idx].next_hop_addr));
    }
    if (i < 0)
    {
        return;
    }

    /* For safety: don't set as reachable if we don't have a LL address yet. Misuse protection. */
    if (neighbor_cache[i].state == ND6_INCOMPLETE || neighbor_cache[i].state == ND6_NO_ENTRY)
    {
        return;
    }

    /* Set reachability state. */
    neighbor_cache[i].state = ND6_REACHABLE;
    neighbor_cache[i].counter.reachable_time = reachable_time;
}
#endif /* LWIP_ND6_TCP_REACHABILITY_HINTS */

/**
 * Remove all prefix, neighbor_cache and router entries of the specified netif.
 *
 * @param netif points to a network interface
 */
void nd6_cleanup_netif(struct netif* netif)
{
    u8_t i;
    s8_t router_index;
    for (i = 0; i < LWIP_ND6_NUM_PREFIXES; i++)
    {
        if (prefix_list[i].netif == netif)
        {
            prefix_list[i].netif = NULL;
        }
    }
    for (i = 0; i < LWIP_ND6_NUM_NEIGHBORS; i++)
    {
        if (neighbor_cache[i].netif == netif)
        {
            for (router_index = 0; router_index < LWIP_ND6_NUM_ROUTERS; router_index++)
            {
                if (default_router_list[router_index].neighbor_entry == &neighbor_cache[i])
                {
                    default_router_list[router_index].neighbor_entry = NULL;
                    default_router_list[router_index].flags = 0;
                }
            }
            neighbor_cache[i].isrouter = 0;
            nd6_free_neighbor_cache_entry(i);
        }
    }
    /* Clear the destination cache, since many entries may now have become
     * invalid for one of several reasons. As destination cache entries have no
     * netif association, use a sledgehammer approach (this can be improved). */
    nd6_clear_destination_cache();
}

#if LWIP_IPV6_MLD
/**
 * The state of a local IPv6 address entry is about to change. If needed, join
 * or leave the solicited-node multicast group for the address.
 *
 * @param netif The netif that owns the address.
 * @param addr_idx The index of the address.
 * @param new_state The new (IP6_ADDR_) state for the address.
 */
void nd6_adjust_mld_membership(struct netif* netif, s8_t addr_idx, u8_t new_state)
{
    u8_t old_state, old_member, new_member;

    old_state = netif_ip6_addr_state(netif, addr_idx);

    /* Determine whether we were, and should be, a member of the solicited-node
     * multicast group for this address. For tentative addresses, the group is
     * not joined until the address enters the TENTATIVE_1 (or VALID) state. */
    old_member = (old_state != IP6_ADDR_INVALID && old_state != IP6_ADDR_DUPLICATED && old_state != IP6_ADDR_TENTATIVE);
    new_member = (new_state != IP6_ADDR_INVALID && new_state != IP6_ADDR_DUPLICATED && new_state != IP6_ADDR_TENTATIVE);

    if (old_member != new_member)
    {
        ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, addr_idx)->addr[3]);
        ip6_addr_assign_zone(&multicast_address, IP6_MULTICAST, netif);

        if (new_member)
        {
            mld6_joingroup_netif(netif, &multicast_address);
        }
        else
        {
            mld6_leavegroup_netif(netif, &multicast_address);
        }
    }
}
#endif /* LWIP_IPV6_MLD */

/** Netif was added, set up, or reconnected (link up) */
void nd6_restart_netif(struct netif* netif)
{
#if LWIP_IPV6_SEND_ROUTER_SOLICIT
    /* Send Router Solicitation messages (see RFC 4861, ch. 6.3.7). */
    netif->rs_count = LWIP_ND6_MAX_MULTICAST_SOLICIT;
#endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
}

#endif /* LWIP_IPV6 */
